Variable cam system

ABSTRACT

A variable cam system which in one embodiment includes cams having a contacting surface formed by an involute curve, a cam shaft, and an actuator for moving the shaft in a longitudinal direction. The operating displacement of the cams may be varied by longitudinally moving the cam shaft.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2004-0107588 filed in the Korean Intellectual Property Office on Dec. 17, 2004, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a variable cam system of a vehicle. More particularly, the present invention relates to a variable cam system for enhancing fuel efficiency and output of a vehicle.

(b) Description of the Related Art

Generally, one or two intake valves and an exhaust valve are mounted to one cylinder of a 4-stroke-cycle engine. An overhead valve type and an overhead cam shaft type of valve opening/closing apparatus is generally utilized. The overhead valve type is where a push rod is pushed by a valve lifter contacted to a surface of a cam of a cam shaft, the push rod operates a rocker arm, and the rocker arm selectively opens/closes a valve. The overhead cam shaft type is where a valve is selectively opened/closed by a cam, which is connected to a cam shaft directly, operating a rocker arm.

However, the foregoing cam system cannot be varied to an optimized position to correspond to a variable running state. Therefore, fuel efficiency and output of a vehicle may deteriorate.

SUMMARY OF THE INVENTION

The present invention provides a variable cam system having advantages of enhancing fuel efficiency and output of a vehicle. An exemplary variable cam system variably opening/closing intake and exhaust valves according to an embodiment of the present invention may include a cam shaft coupled to a timing gear movable in a longitudinal direction thereof, an actuator moving the cam shaft in the longitudinal direction of the cam shaft, and cams secured to the cam shaft to open/close the valves by rotating, a contacting surface of each cam being formed as a curved surface along the longitudinal direction of the cam shaft such that an operating displacement of each cam is varied corresponding to a longitudinal direction movement of the cam shaft. The contacting surface of each cam may be formed as an involute curve. In one embodiment, uppermost points of the contacting surface of each cam may be formed at both ends of the contacting surface of the cam such that an operating displacement of the cam increases as it goes from a center portion, which may be a lower-most point, to either end along the longitudinal direction of the cam shaft, and the uppermost points may deviate from each other by a predetermined angle with respect to a rotating direction of the cam shaft. A bearing may be disposed at an end of a tappet of each valve contacting the contacting surface of each cam. The bearing may be a ball bearing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a variable cam system according to an exemplary embodiment of the present invention.

FIG. 2A and 2B shows a cam of a variable cam system according to an exemplary embodiment of the present invention.

FIG. 3 illustrates an amount of displacement per unit of time of a valve operated by a variable cam system according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENT

An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings.

As shown in FIG. 1, according to an exemplary embodiment of the present invention, a variable cam system variably opening/closing intake and exhaust valves 15 includes a cam shaft 10 defining a longitudinal direction, an actuator 13, and cams 11. The cam shaft 10 is coupled to a timing gear 14 movable in a longitudinal direction of the cam shaft 10 and the actuator 13 moves the cam shaft 10 in the longitudinal direction of the cam shaft 10. The cams 11 are secured to the cam shaft 10 to open/close the valves 15 by rotating, and a contacting surface 16 of each cam 11 is formed as a curved surface in one embodiment along a longitudinal direction of the cam shaft 10 such that an operating displacement of the cam 11 is varied corresponding to a longitudinal direction movement of the cam shaft 10.

As shown in FIG. 1, the timing gear 14 defines a hole 17 that the cam shaft 10 is inserted into and gear teeth may be formed to the hole 17. An end of the cam shaft 10 is inserted into the hole 17 of the timing gear 14 such that the cam shaft 10 can move in the longitudinal direction thereof. Gear teeth corresponding to the gear teeth of the hole 17 of the timing gear 14 may be formed to the end of the cam shaft 10 and a torque is transmitted from the timing gear 14 to the cam shaft 10 by the gear teeth of the hole 17 and the cam shaft 10.

The actuator 13 moves the cam shaft 10 in the longitudinal direction of the cam shaft 10, and in an exemplary embodiment of the present invention, the actuator 13 may be realized as a motor. Actuator 13 may be controlled by a controller based on various appropriate input parameters as may be selected and programmed by a person of ordinary skill in the art.

The timing gear 14 may be connected to a crank shaft (not shown) by a timing chain 18. Therefore, the timing gear 14 receives power from the crank shaft by the timing chain 18.

Each cam 11 rotates by the cam shaft 10 and a tappet 23 is mounted between each cam 11 and the intake/exhaust valves 15. The cam shaft 10 moves in a predetermined range by the actuator 13 such that the tappets 23 can transmit the driving torque of the cams 11 to the intake/exhaust valves 15. The predetermined range in which the cam shaft 10 moves can be varied by a person of ordinary skill in the art.

According to an exemplary embodiment of the present invention, an operating displacement of the cams 11 is varied corresponding to a movement in the longitudinal direction of the cam shaft 10. The operating displacement means a displacement in which each tappet 23 moves up and down by a rotation of each cam 11. That is, as shown in FIG. 1, 2A, and 2B, a contacting surface 16 of each cam 11, which the tappets 23 contact to, may have a different operating displacement depending on a position of the contacting surface 16 of each cam 11.

In one embodiment, the contacting surface 16 of the cams 11 may be formed as an involute curve. An involute curve means a curved line which an end of a thread draws when a thread wound to a cylinder is drawn out therefrom. Therefore, the tappets 23 operate more easily and smoothly by the movement of the cams 11.

As shown in FIGS. 1, 2A and 2B, according to an exemplary embodiment of the present invention, each cam 11 may define two uppermost points 20 which may be at both ends thereof in one embodiment. Tappets 23 operate at a longest operating displacement when the tappets 23 contact to the uppermost points 20. Because, uppermost points 20 of the contacting surface 16 of each cam 11 are formed at both ends of the contacting surface 16 of each cam 11, the operating displacement of each cam 11 increases as it goes from a center portion, which may correspond to a lowermost point 22 in one embodiment, to either end along the longitudinal direction of the cam shaft 10. As shown in FIGS. 2A and 2B, the uppermost points 20 may deviate from each other by a predetermined angle with respect to a rotating direction of the cam shaft 10 (see, e.g., FIG. 2B).

The predetermined angle may be changed and varied by a person of ordinary skill in the art. In one possible embodiment, lowermost point 22 may be formed at a center portion of cam 11 equally spaced between the uppermost points 20.

According to an exemplary embodiment of the present invention, a bearing 12 may be mounted to an end of the tappet 23 of each valve 15. Bearing 12 may be realized as a ball bearing in one possible embodiment. Therefore, each tappet 23 can be more easily contacted to the cams 11 when the cams 11 move rightward and leftward or rotate, and advantageously occurrence of an impact noise by a contact can be reduced and a loss of power by the contact can be minimized.

Referring to FIG. 3, according to an exemplary embodiment of the present invention, a variable cam system is described hereinafter. Because the cam shaft 10 can move in a longitudinal direction thereof, in a rightward and leftward direction in the drawings, the cams 11, having variable displacement, can also move in a rightward and leftward direction together with the cam shaft 10. Therefore, because displacement of the tappets 23 is variably changed, a valve lift and valve timing, that is, displacement of the valves 15 and opening/closing times of the valves 15, may be realized to correspond to variable driving conditions. According to an exemplary embodiment of the present invention, the opening/closing time of each valve and the displacement of each valve may be variably realized corresponding to a shape of the contacting surface 16 of each cam 11. Furthermore, because the contacting surface of each cam 11 is formed as a smooth curved surface, preferably, as an involute curve in one embodiment, an impact noise and an impact vibration can be reduced while the operating displacement varies. Therefore, because variable states of the intake/exhaust valves corresponding to variable driving conditions can be realized, fuel efficiency and output of a vehicle may advantageously be enhanced.

It will be appreciated that the shape of cam 11 and the height and position of the lowermost point 22 and uppermost points 20 may be varied from that shown and described. Therefore, other suitable cam configurations are possible and contemplated according to principles of the present invention.

While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

1. A variable cam system variably opening/closing intake and exhaust valves comprising: a cam shaft coupled to a timing gear movable in a longitudinal direction thereof; an actuator moving the cam shaft in the longitudinal direction of the cam shaft; and a plurality of cams secured to the cam shaft to open/close the valves by rotating, a contacting surface of each cam formed as a curved surface along the longitudinal direction of the cam shaft such that an operating displacement of the cam is varied corresponding to a longitudinal direction movement of the cam shaft.
 2. The system of claim 1, wherein the contacting surface of each cam is formed as an involute curve.
 3. The system of claim 1, further comprising uppermost points on the contacting surface of each cam formed at both ends of the cam such that an operating displacement of the cam increases as it goes from a center portion to either end along the longitudinal direction of the cam shaft; and the uppermost points deviate from each other by a predetermined angle with respect to a rotating direction of the cam shaft.
 4. The system of claim 1, wherein a bearing is disposed at an end of a tappet of each valve contacting the contacting surface of each cam.
 5. The system of claim 4, wherein the bearing is a ball bearing.
 6. A variable cam system for opening and closing intake and exhaust valves comprising: a cam shaft defining a longitudinal direction; an actuator coupled to the shaft and operable to move the shaft back and forth in the longitudinal direction; a plurality of V-shaped cams attached to the shaft in a spaced-apart relationship to each other, each cam having a center portion and an end on either side of the center portion; the ends being higher than the center portion; at least one valve operably coupled to each cam and displaceable by rotational movement of the cam; wherein a relative longitudinal position of each cam is adjustable in relation to each at least one respective valve by the actuator.
 7. The system of claim 6, wherein each valve is connected to a tappet having a bearing at one end that contacts one of the cams, each tappet displaceable up and down by rotational movement of each cam.
 8. The system of claim 6, wherein each cam is shaped as an involute curve.
 9. The system of claim 7, wherein a maximum displacement of each tappet occurs when an end of the cam contacts the bearing.
 10. They system of claim 6, further comprising the actuator including a rack and a pin. 